Year	Years
1970	4.19
1971	4.29
1972	4.38
1973	4.48
1974	4.57
1975	4.67
1976	4.77
1977	4.87
1978	4.98
1979	5.08
1980	5.19
1981	5.3
1982	5.41
1983	5.53
1984	5.64
1985	5.76
1986	5.88
1987	6
1988	6.13
1989	6.26
1990	6.39
1991	6.52
1992	6.66
1993	6.8
1994	6.95
1995	7.1
1996	7.25
1997	7.4
1998	7.55
1999	7.7
2000	7.85
2001	7.99
2002	8.14
2003	8.29
2004	8.44
2005	8.58
2006	8.73
2007	8.87
2008	9.02
2009	9.16
2010	9.31
2011	9.45
2012	9.6
2013	9.74
2014	9.88
2015	10.03